1. Field of the Invention
The present invention chiefly relates to a rust-resistant sleeve that prevents rust and corrosion from developing around the wall of a branch hole when the sleeve is rigidly fitted into the branch hole that is drilled through the wall of a metal conduit such as a water pipeline.
2. Description of the Related Art
A rust-resistant sleeve is known and in widespread use in water supply systems. Such a rust-resistant sleeve is fitted into a branch hole drilled into the wall of a water pipeline to attain rust and corrosion resistance in the inner surface of the pipeline.
Many of these rust-resistant sleeves are metal sleeves made of copper (phosphor-deoxidized copper), stainless steel or the like, and are directly fitted into a branch hole drilled into the wall of a water pipeline. When the sleeve is installed into the pipeline, undue force may work on the sleeve, causing it to be deformed. Such a deformation creates an insufficient contact between the inner wall of the branch hole and the metal sleeve, thereby causing the sleeve to fail to achieve a good rust resistance performance. In a preventive step, the outer circumference of the metal sleeve is coated with an elastic member such as synthetic rubber.
Since the water pipeline presents naturally a high moisture and splashy environment, the elastic member has preferably a water absorption property to prevent rust development. Conventionally available high-water-absorption materials such as starch-acrylic ester graft, cross-linked carboxymethyl-cellulose, and cross-linked polyvinyl alcohol are used in agriculture fields (for example for soil improvements in water retaining property), in sanitation and medical fields.
A water absorbing rubber into which one of these high-water-absorption resins and SBR (styrene-butadiene rubber) or EPDM (ethylene-propylene-dienemetylene linkage) rubber are blended is occasionally used in civil engineering fields and building construction as dehydrating or sealing compound.
Even if the metal sleeve is covered or coated with an elastic member such as the above rubber for rust resistance, the elasticity of the rubber only serves the contact between the sleeve and the inner wall of the branch hole. To fit the sleeve into the branch hole, the sleeve has to be partly or uniformly expanded in diameter to press firmly the rubber around the circumference of the sleeve, against the inner wall of the branch hole, using a stretching tool. When the deformation of the metal sleeve becomes irregular during the cut and expansion step, an undue external force may destroy partly the rubber, and rust resistance performance is thus degraded.